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| Home > Publications database > Herstellung von Elektrodenstrukturen für Lithium-Ionen-Dünnschichtbatterien |
| Dissertation / PhD Thesis/Book | FZJ-2015-05402 |
2015
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
ISBN: 978-3-95806-073-9
Please use a persistent id in citations: http://hdl.handle.net/2128/9086
Abstract: The aim of this work is to prepare electrode structures which are suitable for the application in lithium-ion thin film batteries. If in lithium-ion batteries a thin film solid electrolyte is used instead of liquid electrolyte, the safety, lifetime and energy density can be increased. To get a complete coverage by the solid electrolyte free of any defects, an electrode with a microscopic smooth surface is needed. Electrodes with this property can be produced by physical vapour deposition. Lithium iron phosphate (LiFePO$_{4}$) is chosen as the electrode material. The identifying features of LiFePO$_{4}$ are environmental sustainability, low costs and a high safety. LiFePO$_{4}$ thin films were obtained by magnetron sputtering which can be assigned to the physical vapour deposition techniques. This thesis shows that an interaction between substrate and deposited thin film can severely affect the morphology of the sample. On titanium as well as on aluminium iron-rich particles grow on the surface of the deposited thin-film. Some of the iron-rich particles on the surface of the deposited LiFePO$_{4}$ thin film on titanium have a rod-shape structure with lengths of several hundredths of nanometres. An interdiffusion between the titanium substrate and the deposited LiFePO$_{4}$ thin film is proved by secondary ion mass spectrometry (SIMS). By using a titanium nitride interlayer the interdiffusion between titanium and deposited thin film is remarkably reduced. No iron-rich particles grow on the surface which is leading to microscopic smooth surface that can be coated with a thin film solid electrolyte by physical vapour deposition. In comparison with the direct deposition of the LiFePO$_{4}$ thin film on titanium, titanium nitride interlayers avoid additionally the formation of further impurity phases. Furthermore, titanium nitride has a positive influence on the crystallisation behaviour and improves the electrochemical performance for thin films with thicknesses of 80 nm and 160 nm. At thicknesses of 320 nm the electrochemical performance on titanium is superior. But in general, only a small amount of the theoretical capacity is used. To enhance the electrochemical performance, LiFePO$_{4}$ thin films with additional carbon (LiFePO$_{4}$ +C) have been deposited. These thin films have an increased utilization. However, the increase in utilization cannot be related only to the carbon present in the thin film, it can also be related to the morphology of the thin film. With increasing deposition time a fibre-like structure develops which has a much larger surface area. LiFePO$_{4}$ +C thin films with a smooth surface have comparable capacities to that of pure LiFePO$_{4}$ thin films. The capacity is increased only after the fibre-like structure has developed.
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